The invention relates to a rotor for a high speed permanent magnet motor. In particular, the invention concerns a motor rotor comprising a plurality of magnetic discs stacked on a central spindle, a clamping device provided to exert an axial clamping force on said magnetic discs to form an axially pre-tensioned disc packet, wherein each of said magnetic discs is provided with at least one electrically insulating layer for electrical separation relative to adjacent discs or to said clamping device.
It is a fact that permanent magnetic materials used in motor rotors are exposed to a high centrifugal stress, and that the tension strength limit of such materials is easily reached at high speed operation. This means that permanent magnetic rotors have to be reinforced to cope with the high centrifugal stresses generated at high speed operation.
A previously known method to reinforce permanent magnet rotors is to provide an outer sleeve enclosing the permanent magnetic material parts of the rotor. Such sleeve may comprise a high-strength metal tube made of a non-magnetic material like titanium, cold worked stainless steel, etc. or may be formed of a high-strength fiber bandage wound around the permanent magnet parts of the rotor. In both cases the reinforcement is radially pre-tensioned to minimize the tension stress on the magnetic material caused by centrifugal forces during operation of the motor.
In small diameter rotor applications, an outer reinforcement sleeve is undesirable since it adds to the diameter of the rotor. It is undesirable also from the manufacturing cost point of view, because the sleeve not only adds one or more details to the rotor, it also adds a number of extra working operations when assembling the rotor.
In order to solve the above-mentioned problems, the present invention provides a permanent magnet rotor which does not have any outer sleeve. Instead, the permanent magnet rotor of the present invention comprises a reinforcement means which does not influence the diameter of the rotor and which does not complicate the assemblage of the rotor.